Cancel my contract!!!!!!!

I took out a Sim card with mtn and isn't want to use it after 2 months. Well I have never used it. So I went to Mtn carnival city to cancel. I was put on the phone and advised to pay an amount for closure which I did. When I called back to cancel they said they now owed me a certain amount which I didnt care about as I want to cancel because another invoice is raised. I have been on the phone with Mtn for 3 weeks trying to cancel and everytime I get cut or they hang up. No one even bothers to call me back. They said I need to speak to Legal department who doesn't have a direct line and no one can put me through. I have waited my own airtime each time to call holding for minutes and even an hour at times and still to this day the contract is not cancelled. I Dont know what to do anymore as Mtn is forcing me to keep the contract I have never used. I'm so irritated by the whole process